This invention is directed to a drill bit structure capable of drilling holes in ceramics, glasses or other hard, brittle materials. More particularly, the drill bit includes a pilot element which forms a hole of a first, small dimension and an enlarging means which subsequently passes through this hole and forms a larger hole of the finished desired dimension.
It is exceedingly difficult to drill holes and the like in hard, brittle materials such as glasses, ceramics, hard cyrstalline structures and the like. Presently, two types of drills are predominantly utilized to form holes in these materials.
The two types of drills commonly utilized are the spear point drill and the core drill. The spear point drill, as its title implies, is shaped much like a spear point. The core drill has a hollow core with a cylindrical cutting edge surrounding the core. With core drills, the use of a coolant or the like is necessary. Neither of the above types of drills, however, are totally satisfactory in their performance and use.
As is evident from considering the rotation of anything, starting at the center of rotation and moving radially from the center of rotation, as an object revolves at a fixed rate of rotation, the velocity of any particular point of that object along the circular path in which the point moves increases as one moves radially away from the center of rotation. Thus, a point located on the periphery of the object is moving along the circular pathway at a greater velocity than a point midway between the center of rotation and the periphery, and at the exact center of rotation the velocity approaches zero.
If one considers a size domain, such as the domain represented by the size of typical cutting grits which might be so located on such a surface, a particular piece of grit located exactly at the center of rotation will, in fact, only rotate, and not move in a circular pathway. A next piece of grit, immediately adjacent but radially displaced from the center of rotation from this first piece of grit, will move in a circular pathway at a very low velocity. As the pieces of grit progress outwardly, the individual pieces of grit start moving at higher and higher velocities in their particular circular pathways.
With a spear point drill having cutting grit on its surfaces, the cutting grit located at the exact center point is in continuous contact with the surface being cut, and because the velocity (in a circular pathway) at the exact center point is low, the cutting grit at and near the center point is involved in a chipping and chiseling type operation. At a greater radial displacement from the center of rotation further up the surface of the spear point, the particles of the cutting grit are moving in their circular pathways at a greater velocity, and as a result of this, these particles cut by high velocity scratching of the surface being cut.
A chipping and chiseling type of cutting can lead to cracks and other stresses in the material being cut. It further leads to "wear" of the tool at and near its point.
Current problems with the currently utilized types of drills for glasses and the like thus include cracks or cataclysmic shattering of the materials being drilled with the spear point drills, and in a further instance, the necessity of using coolants in combination with core drills preclude their use except where bench or other similar type setups are available which can include the use of the coolant.
Because of the above disadvantages of the currently utilized drill bits for cutting glass, ceramics or other hard, brittle materials, it is believed that there exists a need for new and improved drill bits for forming holes and the like in these types of materials. Furthermore, there exists a need for a drill bit which is portable and capable of being utilized in common hand drills, portable power drills and the like without the necessity of complex setups and the presence of coolants and the like.